The present invention relates to digital communication systems. More particularly, and not by way of limitation, the invention relates to a system and method for managing locally administered Media Access Control (MAC) addresses in an Ethernet Local Area Network (LAN).
Ethernet is a packet-based transmission protocol that is primarily used in LANs. Ethernet is the common name for the IEEE 802.3 industry specification. Data is transmitted in Ethernet frames, and FIG. 1 is an illustration of a typical Ethernet frame 10. To synchronize the receiving node(s), each frame starts with 64 bits used only for synchronization, consisting of a 56-bit preamble 11 and an 8-bit Start of Frame Delimiter (SFD) 12. A destination address 13, a source address 14, and a length/type identifier 15 follow the preamble. Media Access Control (MAC) client data 16, together with a Packet Assembler/Disassembler (PAD) 17 may vary in length from 46 to 1500 octets. A Frame Check Sequence (FCS) 18 adds four more octets. The frame size is counted from the destination address to the FCS, inclusive, and thus may vary between 64 and 1518 octets, not including an optional Virtual Local Area Network (VLAN) tag, which adds 4 octets.
FIG. 2 is an illustration of a typical Ethernet destination and source address structure, known as a MAC address, as shown in IEEE 802.3, which is incorporated herein by reference. An I/G field 21 indicates whether the address is an individual or a group address. A zero (0) in this field indicates an individual address, while a one (1) indicates a group address (multicast). Note that a source address can only have a zero (0) in the I/G field. A U/L field 22 indicates whether the address is a universal or local address. A zero (0) in this field indicates a universally administered address, while a one (1) indicates a locally administered address. A destination address with all ones represents a broadcast address. The MAC address structure is completed with the actual address bits 23.
FIG. 3 is an illustration of a globally administered, Unit-unique MAC address 30, as shown in IEEE standard 802-1990, which is incorporated herein by reference. An Organizationally Unique Identifier (OUI) 31 is assigned to each global MAC address to ensure uniqueness. The OUI is a 3-octet hexadecimal number that is used as the first half of a 6-octet MAC address. An organization using a given OUI is responsible for ensuring uniqueness of the MAC address by assigning each produced unit its own unique 3-octet Unit-unique MAC address 32.
FIG. 4 is an illustration of a locally administered MAC address 40. IEEE standard 802.3 describes how to ensure unique MAC addresses for locally administered addresses by assigning “1” and “0” as the two least significant bits (LSB) of the first transmitted octet 41. These bits are also shown as 21 and 22 in FIG. 2. The bit “1” indicates that the address is a locally administered address, and the bit “0” indicates that it is a unicast address. However, IEEE standard 802.3 fails to disclose any method of ensuring unique locally administered MAC addresses when several nodes operate autonomously, or when several nodes belonging to separate solutions operate in the same Ethernet network utilizing locally administered addresses. The present invention provides a solution to this shortcoming.